1. Field of the Invention
The present invention relates to solid-state image sensing devices. More particularly, this invention relates to apparatus and methods that generate signals for activating and controlling operation of multiple photosensor solid state image sensing devices.
2. Description of Related Art
Integrated circuit image sensors are finding applications in a wide variety of fields, including medical endoscopy, machine vision, robotics, guidance and navigation, automotive applications, and consumer products such as digital camera and video recorders. Imaging circuits typically include a two dimensional array of photo sensors. Each picture element (pixel) of the image includes at least one photo sensor. Light energy emitted or reflected from an object impinges upon the array of photo sensors. The light energy is converted by the photo sensors to an electrical signal. Imaging circuitry scans the individual photo sensors to read out the electrical signals. The electrical signals of the image are processed by external circuitry for subsequent display.
Modern metal oxide semiconductor (MOS) design and processing techniques have been developed that provide for the capture of light as charge and the transporting of that charge within active pixel sensors and other structures so as to be accomplished with almost perfect efficiency and accuracy.
One class of solid-state image sensors includes an array of active pixel sensors (APS). An APS is a light sensing device with sensing circuitry inside each pixel. Each active pixel sensor includes a sensing element formed in a semiconductor substrate and capable of converting photons of light into electronic signals. As the photons of light strike the surface of a photoactive region of the solid-state image sensors, free charge carriers are generated and collected. Once collected the charge carriers, often referred to as charge packets or photoelectrons, are transferred to output circuitry for processing.
An active pixel sensor also includes one or more active transistors within the pixel itself. The active transistors amplify and buffer the signals generated by the light sensing element to convert the photoelectron to an electronic signal prior to transferring the signal to a common conductor that conducts the signals to an output node.
Active pixel sensor devices are fabricated using processes that are consistent with complementary metal oxide semiconductor (CMOS) processes. Using standard CMOS processes allows many signal processing functions and operation controls to be integrated with an array of active pixel sensors on a single integrated circuit chip.
Active pixel sensor devices generally include at least one active transistor that is used to reset or clear the devices of charge from a previous image before the capturing the next image. In the rolling shutter operation, as described in U.S. Pat. No. 6,809,766 (Krymski, et al.), each row of active pixel sensors of the array is reset to clear the charge from the sensor and optionally a storage node of the device. The row is then exposed to light impinging upon the array for an integration time and then read out to convert the photoelectrons to the image data for the row.
Alternately, in a global shutter, as shown in U.S. Pat. No. 6,667,768 (Fossum), all rows of active pixel sensors of the array are reset to clear the charge from the sensor and optionally a storage node of the device. The row is then exposed to light impinging upon the array for an integration time. Each row is then read out to convert the photoelectrons to the image data for the row.
“A CMOS Image Sensor with a Double-Junction Active Pixel”, Findlater, et al., IEEE Transactions on Electron Devices, January 2003, Vol.: 50, Issue: 1, pp: 32-42 describes a CMOS image sensor that employs a vertically integrated double-junction photodiode structure. This allows color imaging with only two filters. The sensor uses a 6-transistor pixel array.
“CMOS Image Sensor with NMOS-Only Global Shutter and Enhanced Responsivity”, Wany, et al., IEEE Transactions on Electron Devices, January 2003, Vol.: 50, Issue: 1, pp: 57-62, provides an NMOS-only pixel with a global shutter and subthreshold operation of the NMOS sample-and-hold transistor to increase optical responsivity.
“A High-Dynamic-Range CMOS Image Sensor for Automotive Applications, Schanz, et al., IEEE Journal of Solid-State Circuits, July 2000, Vol: 35, Issue: 7, pp: 932-938 describes a CMOS imager that uses a combination of a multiexposure and a multigain linear read out.
U.S. Pat. No. 6,107,655 (Guidash) illustrates an image sensor having an array of pixels with at least two row adjacent pixels and at least two column adjacent pixels. At least one electrical function is integrated within the adjacent pixels and is shared between the adjacent pixels. The electrical function can be either a contact region or an electrical circuit used in implementing either a photogate, a transfer gate, a reset gate, a row select gate, an amplifier drain, an output node, a floating diffusion contact, a reset drain, a lateral overflow gate, an overflow drain or an amplifier.